Filter media

ABSTRACT

A filter media comprising a synthetic microfiber polymer fine fiber web wherein the diameter of the fibers is between about 0.8 to about 1.5 microns. The filter media is acceptable for use in ASHRAE applications. Constructions with a low DP backing, support or prefilter layers of coarse fiber provide large area filter webs of high efficiency and a stable and high threshold value of alpha above eleven.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 09/698,584, filed on Oct. 27. 2000, now U.S. Pat. No.6,554,881, which claims priority to U.S. Provisional Patent ApplicationNo. 60/162,545, filed on Oct. 29, 1999 and U.S. Provisional PatentApplication No. 60/178,348, filed on Jan. 25, 2000, the contents ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to air filters, and more specificallyto a non-woven filter composite and a method for forming the composite.

BACKGROUND OF THE INVENTION

The removal of air borne contaminants from the air is a concern toeveryone. Gas phase filtration has traditionally been accomplished bymethods which utilize activated carbon. One approach has been to use acarbon/adhesive slurry to glue the carbon to a substrate. However, theadhesive decreases carbon performance by forming a film on its surface.A second approach involves carbonizing an organic based web by heating,followed by carbon activation. This material has a high cost and hasrelatively low adsorption capacity. A third approach involves forming aslurry of carbon powders and fibers into sheets by a process analogousto a wet papermaking process. This material is medium-to-high cost, andhas an undesirable high pressure drop.

Alternatively, carbon particles have been treated with chemicals toincrease uptake of air contaminants. However, chemical treatment is notefficient when used in conjunction with an aqueous process, as theaqueous nature of the process either washes away the chemical used toimpregnate the carbon, or reacts undesirably with the impregnatingchemical rendering it useless. However, filter materials which do notincorporate chemical absorbents into the carbon particles perform farless effectively than those which do include chemically impregnatedabsorbents.

Another approach to entrain air contamination has been to produce low,medium and high efficiency pleatable composite filter media whichinclude either a low, medium or high efficiency fibrous filtration layerof randomly oriented fibers; and one or more permeable stiffening layerswhich enable the composite filter media to be pleated and to sustain itsshape. Such filtration devices serve as vehicle passenger compartmentair filters, high performance engine air filters and engine oil filters.ASHRAE (American Society of Heating Refrigeration and Air ConditioningEngineers) pleatable filters and the like typically use a pleated highefficiency filtration media for the filtration element.

Currently, the pleated high efficiency media normally used in thesefiltration devices are made from ASHRAE filter media or paper products.These paper products are made by a wet-laid technique wherein fibers,e.g. glass or cellulosic fibers, are dispersed in an aqueous binderslurry which is stirred to cause the fibers to become thoroughly andrandomly mixed with each other. The fibers are then deposited from theaqueous binder slurry onto a conventional paper making screen or wire asin a Fourdrinier machine or a Rotoformer machine to form a matted paperwhich includes a binder resin, e.g., a phenolic resin. Pleated filterelements made from such papers can exhibit high efficiencies. However,these pleated filter elements have low dirt-holding capacities andexhibit high pressure drops.

Electrostatically charged synthetic filter media is also used in thesefiltering applications, and these can attain very high filtration versuspressure drop performance characteristics, at least in their initialcharge state. However, during use many of these products lose theirelectrostatic charge, or it is masked by deposits, causing filtrationefficiency to drop substantially, sometimes to levels below what isacceptable.

Accordingly, there remains a need to provide a relatively low cost, highefficiency filter media for these filtration applications which exhibitrelatively high dirt-holding and/or air contaminant capacities andrelatively low pressure drops as well as low and medium efficiencyfilter media which exhibit relatively high dirt-holding capacities andrelatively low pressure drops.

SUMMARY OF THE INVENTION

The present invention circumvents the problems described above byproviding fiber webs and filter composites which retain particles, airborne contaminants, and/or oil without reduction in filtrationperformance below a high base threshold even after prolonged filtrationchallenges. In a particular embodiment, the filter media of the presentinvention is a polymeric fiber web having a fine fiber layer on acoarser support, and which, after decay of any charge which may bepresent, possesses an alpha above about 11, i.e. 13 or 14. The web caninclude an antioxidant within the web matrix. Accordingly, the presentinvention provides filter media, useful in filtering applications suchas air conditioning, ventilation and exhaust ducts as bag filters orpleated panel filters, which relies upon mechanical filtrationproperties rather than electrostatic charge for its base level offiltration efficiency, thus providing filter media which have enhancedfiltration performance characteristics, such as efficiency versuspressure drop characteristics over time.

The present invention comprises a cost effective, high efficiency, lowpressure drop, adsorptive, non-woven filter media comprising a highsurface area synthetic microfiber, e.g., melt blown, fine fiber layer.The filter media can also include one or more non-woven spun bond layersand can be combined with a coarse fiber support layer. The coarse fibersupport layer can itself be a low pressure drop synthetic microfiber,e.g., melt blown, layer adhered to a spun bond layer, and can serve as aprefilter to enhance overall performance. The invention alsocontemplates a method for forming the filter media comprising dryapplication of the non-woven fine fiber filter media to the non-wovencarrier material. Various layers can be calendared, and the completemultilayer web assembled with heat, with or without a cover sheet.

In one exemplary method of manufacture, a polypropylene resin isextruded by a melt pump through a die having a plurality of extrusionholes to produce large diameter fibers into a stream of hot air whichstretches the fibers to a diameter well below several microns andcarries them toward a collector belt passing over a vacuum box oppositethe extrusion head. Preferably a spun bond mat or web is carried by thecollector belt so that the melt-blown fine fibers land on and accumulateon the spun bond layer to produce a large area matrix of filtrationmaterial on a support. This material can be used directly on a suitablestructural support, or can be further bonded to another layer of coursenon-woven fibrous support material to form a large area filter mediasuitable for a variety of commercial uses. Alternatively, the syntheticmicrofiber fine fibers can be used alone, and the web carried on thecollector belt is used only to collect the blown fibers. The syntheticmicrofiber fine fibers of the invention have an alpha value of at leastabout 11 or more, i.e., 13 or 14. In a particularly preferredembodiment, the synthetic microfiber fine fibers have an alpha valuewhich remains constant or stable over time. The synthetic microfiberfine fiber web can be calendered to enhance fiber entanglement. In apreferred embodiment, the synthetic microfiber is a melt blown fiber.

In one embodiment, the present invention pertains to filter media whichinclude an effective filtration layer of synthetic microfiber which neednot be charged. The actual diameter of the fibers of the syntheticmicrofiber material is between about 0.8 to about 1.5 microns, i.e. 1.0microns, as measured by scanning electron microscopy, and in a preferredembodiment, the synthetic microfiber, e.g., melt blown, polymericmaterial is a polypropylene, e.g., Exxon PP3456G (Exxon, Houston, Tex.)having a melt flow of about 1200, which contains an antioxidant.Preferably the fine fiber has a web basis weight of between about 6 g/m²and about 25 g/m², and is generally applied over a coarser support orstrengthening layer of low solids such that the web has an alpha valueof at least about 11 or more, i.e., 13 or 14. The synthetic microfiberfine fibers of the invention have a 60-65% ASHRAE (at a basis weight ofabout 6 to about 12 g/m², e.g., 8 g/m²), 80-85% ASHRAE (at a basisweight of about 15 g/m² to about 22 g/m², e.g., 18 g/m²) and 90-95% (ata range of about 18 g/m² to about 25 g/m²). In a particularly preferredembodiment, the polymer fiber web has an alpha value which remainsconstant or stable over time.

In another embodiment, the present invention pertains to filter mediawhich include a synthetic microfiber, e.g., melt blown, polymer finefiber layer which is substantially uncharged, and at least one spun bondfiber or coarse fiber support layer. The diameter of the syntheticmicrofiber fine fibers is between about 0.8 to about 1.5 microns, i.e.1.0 microns, and the spun bond or coarse fiber layer acts as a support,prefiltering or strengthening layer. As applied to the upstream side ofthe filter in a vent or air conditioning flow, the spun bond fiber layercan have a basis weight of between about 5 g/m² and 10 g/m², e.g., 8.5g/m², and serves as a prefilter. As applied to the downstream side, itcan be applied in a layer two to four times more massive, enhancing itsfunction as a support web. The stiffer backing can have a basis weightbetween about 34 g/m² and about 55 g/m², i.e., 40.8 g/m² and about 54.4g/m²). Typically the spun bond material is selected from polyesters,polyethylene, polypropylene, or polyamide polymers, and is assembledwith the fine fiber layer such that the filter media composite has analpha value of about 11 or more, i.e., 13 or 14. In a preferredembodiment, the spun bond layer is made of a polypropylene resinmanufactured by Reemays. For example, a preferred polypropylene spunbond support with a basis of weight of 40.8 g/m² is fabricated fromTYPAR 3121N (Reemay, Old Hickory, Tenn.) and for a polypropylene spunbond support with a basis weight of about 54.4 g/m² is fabricated fromTYPAR 3151C (Reemay, Old Hickory, Tenn.).

Alternatively, a coarse synthetic microfiber, e.g., melt blown, materialwhich serves as a prefilter can be used as a support and typically has abasis weight between about 50 g/m² to about 100 g/m², e.g., 80 g/m²,with a fiber diameter of between about 5 and about 20 microns, e.g.,between about 13 and about 17 microns, e.g., between about 13 and 15microns. For example, the coarse melt blown material can be made from apolypropylene resin having a melt flow of 1200 (polypropylene resinPP3546G, Exxon, Houston, Tex.) or, preferably, a polypropylene having amelt flow of 400 (polypropylene resin HH441, Montell Polymers,Wilmington, Del.). The coarse synthetic microfiber is assembled with thefine fiber layer such that the filter media composite has an alpha valueof at least about 11 or more, i.e., 13 or 14.

The combination of the synthetic microfiber, e.g., melt blown, finefiber with the spun bond fiber layer or coarse synthetic microfiber,e.g., melt blown, layer in a web is unique in that no bonding agents,e.g., adhesives, are required to adhere the two materials to each other.Typically, the two layers are pressed together by a calendering processwhich causes each layer to physically adhere to the other layer. Thisprovides the advantage that a bonding agent is not incorporated into thecomposite and does not effect the porosity of the composite filtermedia.

In still another embodiment, the present invention pertains to filtermedia which includes a substantially uncharged synthetic microfiberlayer that can provide an effective degree of filtration when charge, ifany, is dissipated, a spun bond fiber layer and a coarse support fiberlayer. Generally, the actual diameter of the synthetic microfiber finefibers is between about 0.8 to about 1.5 microns and preferably aboutone micron, and the coarser support fiber layer acts as a support forthe finely enmeshed fine fiber web material. Typically the coarsesupport fiber layer is made of polymers which can also be blown but havelower solids and can, for example have a much higher stiffness andgreater fiber diameter. The coarse synthetic microfiber material whichserves as a prefilter has a basis weight between about 20 g/m² to about100 g/m², e.g., 80 g/m², with a fiber diameter of between about 5 andabout 20 microns, e.g., between about 13 and about 17 microns, e.g.,between about 13 and 15 microns. For example, the coarse syntheticmicrofiber material can be made from a polypropylene resin having a meltflow of between about 400 and about 1200. For example, a suitablepolypropylene resin with a melt flow of 1200 is the polypropylene resinPP3546G, available from Exxon (Houston, Tex.). Preferably, apolypropylene resin having a melt flow of 400 is available from MontellPolymers (Wilmington, Del.), designated as HH441. Preferably, the finefiber layer is applied to the coarser layers to produce a filter mediacomposite having an alpha value of at least about 11, i.e. 12, 13 or 14.In a preferred embodiment, the synthetic microfiber is a melt blownfiber.

The present invention also pertains to filter media which include afirst spun bond fiber layer, a substantially uncharged syntheticmicrofiber layer, a coarse support fiber layer and a spun bond supportfiber layer. It should be understood that additional layers of eachmaterial can be included to form the final composite filter media webfor particular applications or strength requirements. It should also beunderstood that the order of layers can be switched so long as thelayers are assembled so that an alpha of 11 or more, i.e., 13 or 14, isachieved in the uncharged or charge-decayed state, and typically, thesynthetic microfiber fine fiber filter media has fibers of a diameter ofbetween about 0.8 to about 1.5 microns. In general, the filter media ofthe present invention can be fabricated in a range, e.g., with particlepenetrations of 60-65 percent ASHRAE, 80-85 percent ASHRAE, or 90-95percent ASHRAE, while still achieving the combination of effectivefiltration for the level of pressure drop. In representative examplesbelow, the amounts of fine fiber can be varied for the differentembodiments.

All percentages by weight identified herein are based on the totalweight of the web unless otherwise indicated.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages and features of the present invention will bereadily appreciated as the same becomes better understood by referenceto the following detailed description when considered in connection withthe accompanying drawings, in which like reference numerals designatelike parts throughout the figures thereof and wherein:

FIG. 1 is a schematic, sectional view of a filter media according to thepresenting invention;

FIG. 2 is a schematic, sectional view of a filter media according toanother embodiment of the invention;

FIG. 3 is a schematic, sectional view of a filter media according to yetanother embodiment of the invention; and

FIG. 4 illustrates a preferred process and system for manufacturingfilter media.

DETAILED DESCRIPTION OF THE INVENTION

The features and other details of the invention will now be moreparticularly described and pointed out in the claims. It will beunderstood that the particular embodiments of the invention are shown byway of illustration and not as limitations of the invention. Theprinciple features of this invention can be employed in variousembodiments without departing from the scope of the invention.

The present invention circumvents the problems described above byproviding fiber webs and filter composites which retain particles, airborne contaminants, and/or oil without significant reduction infiltration performance even after prolonged filtration challenges. In aparticular embodiment, the filter media of the present invention is apolymeric fiber web that can include an antioxidant within the webmatrix. The fine fiber layer, can for example, be uncharged or can allowdecay of charge introduced during manufacture, and is supported on a lowsolids matrix to provide a filter web to provide a high alpha value.Alpha values are the normalized measure of filter penetration andpressure drop used to rate filters. Accordingly, the present inventionprovides uncharged filter media useful for use in a variety of airfiltration applications, including heating and air conditioning ducts asbag filters or pleated panel filters. The invention also provides filtermedia which have enhanced filtration performance characteristics.

The present invention comprises a cost effective, high efficiency, lowpressure drop, adsorptive, non-woven filter composite comprising a highsurface area synthetic microfiber, e.g., melt blown, web and can includeone or more non-woven spun bond layers and/or coarse fiber support(s).The invention also contemplates a method for forming the melt blownpolymer fiber web and composites thereof comprising dry application ofthe non-woven filter media to the non-woven carrier or support material,which can be heated and calendared with or without a cover sheet.

In one embodiment, the present invention pertains to filter media whichinclude a substantially uncharged synthetic microfiber web. The diameterof the fibers of the synthetic microfiber material is between about 0.8to about 1.5 microns, preferably between about 0.9 and 1.5 microns witha most preferred diameter of about one micron, as measured by scanningelectron microscopy. In a preferred embodiment, the fibers of thesynthetic microfiber material have an average range between about 0.8and about 1.5 microns. Optical measurements can appear of somewhatlarger dimension, but the fine fibers should be under several microns.In a preferred embodiment, the synthetic microfiber polymeric materialis polypropylene, although other materials, and even materials such aspolyethylene, polybutylene and/or any other polymers which do notinherently possess a charge, such a nylons, can be serviceable. Oneexample of a suitable polypropylene material is available from ExxonCorporation as Exxon PP3456G, a proprietary polypropylene resincomposition which contains approximately 0.06 to 0.12 percent of anantioxidant, about 475-690 ppm peroxide, 35-70 ppm of a neutralizer andhas a melt flow of about 1200. In a preferred embodiment, the syntheticmicrofiber is a melt blown polymeric material.

The fine fiber web can have a weight basis of between about 6 g/m² andabout 25 g/m², e.g., 8 g/m², 18 g/m², or 22 g/m², although in otherembodiments this layer can have a web basis of up to about 100 g/m², andhas an alpha value, as measured after elimination of any residualelectrostatic charge, of at least about 11, i.e., 12, 13 or 14. In aparticularly preferred embodiment, the polymer fiber web has a thresholdalpha value which remains substantially constant over time aftereliminating any residual electrostatic charge. The fine fiber filtermedia of the present invention can be fabricated in a range, e.g., withparticle penetrations of 60-65 percent ASHRAE, 80-85 percent ASHRAE, or90-95 percent ASHRAE, while still achieving the combination of effectivefiltration for the level of pressure drop.

The phrase “synthetic microfibers” is well recognized in the art and isintended to include those fibers which are prepared from polymers havinga diameter of about 0.1 micron to about 20 microns, preferably fromabout 0.1 micron to about 12, and most preferably from about 0.5 micronsto about 5 microns, e.g., an average diameter in the range of about 0.8to about 1.5 microns. In general, the length of the microfibers is fromabout 0.01 millimeters to continuous, preferably from about 0.1millimeter to continuous, most preferably from about 5 millimeters tocontinuous. More generally, the length of the fibers fall within therange of from about 0.1 millimeters to about 25 millimeters, morepreferably from about 0.1 millimeters to about 10 millimeters and mostpreferably from about 1 millimeter to about 7 millimeters. Syntheticmicrofibers include those known as melt blown fibers, spun bond fibers,meltspun fibers, solutionspun fibers, microfilaments, split fibers andelectrospun fibers.

The term “melt blown fibers” is recognized by those having ordinaryskill in the art and as used herein indicates fibers formed by extrudinga molten thermoplastic polymer through a plurality of fine, usuallycircular, die capillaries as molten threads or filaments into a highvelocity gas stream which attenuate the filaments of moltenthermoplastic polymer to reduce their diameter. As is known in the art,the flow rate and pressure of the attenuating gas stream can be adjustedto form continuous melt blown filaments or discontinuous fibers. Theformed air-borne fibers, which are not fully quenched, are carried bythe high velocity gas stream and deposited on a collecting surface toform a web of randomly dispersed and autogenously bonded melt blownfibers. Exemplary processes for producing melt blown fiber web aredisclosed in U.S. Pat. No. 3,849,241 to Butin et al. and U.S. Pat. No.4,380,570 to Schwarz. In general melt blown fibers have an average fiberdiameter of up to about 10 micrometers.

Melt blown materials fall in the general class of textiles referred toas nonwovens as they comprise randomly oriented fibers made byentangling the fibers through mechanical means. The fiber entanglement,with or without some interfiber fusion, imparts integrity and strengthto the fabric. The nonwoven fabric can be converted to a variety of enduse products as mentioned above, e.g., pool filters.

The term “spunbond fibers” is recognized by those having ordinary skillin the art and as used herein indicates small diameter filaments thatare formed by extruding one or more molten thermoplastic polymers asfibers from a plurality of capillaries of a spinneret. The extrudedfibers are cooled while being drawn by an eductive or other well-knowndrawing mechanism to form spunbond fibers. The drawn spunbond fibers arethen deposited or laid onto a forming surface in a random manner to forma loosely entangled and uniform fiber web. The laid fiber web is thensubjected to a bonding process, such as thermobonding or byneedlepunching, to impart physical integrity and dimensional stability.Typically, spunbond fibers have an average diameter of at least about 10microns. Exemplary processes for producing spunbond nonwoven webs aredisclosed, for example, in U.S. Pat. No. 4,340,563 to Appel et al., U.S.Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. No. 3,855,046 to Hansenet al. and U.S. Pat. No. 3,692,618 to Dorschner et al. Spunbonded websare characterized by a relatively high strength/weight ratio, highporosity, have abrasion resistance properties and are typicallynon-uniform in such properties as basis weight and coverage.

Spunbonded polymeric nonwoven webs can be produced by extruding polymerthrough a die to form a multiplicity of continuous thermoplastic polymerstrands as the polymer exits holes in the die in a generally downwarddirection onto a moving surface where the extruded strands are collectedin a randomly distributed fashion. The randomly distributed strands aresubsequently bonded together by to provide sufficient integrity in aresulting nonwoven web of continuous fibers.

The term “meltspun fibers” is recognized by those having ordinary skillin the art and includes those fibers produced, for example, by U.S. Pat.No. 5,114,631 to Nyssen et al. or U.S. Pat. No. 4,937,020 to Wagner etal. In short, molten polymer is spun radially from a rotating nozzlehead producing fibers from 0.1 to 20 microns.

The phrase “solution spun fiber” is recognized by those having ordinaryskill in the art and includes, for example, those fibers produced byU.S. Pat. No. 4,734,227 to Smith. These fibers are produced from asolution containing supercritical fluid solvent where polymer is rapidlyexpanded through a nozzle forming ultrafine fibers of 1 to 5 microndiameter.

The term “microfilaments” is recognized by those having ordinary skillin the art and is intended to include those fibers produced by theprocess detailed in U.S. Pat. No. 4,536,361 to Torobin. This processprovides that a molten polymer is formed into a hollow tube and whilethe hollow fiber is still molten, it is contacted with an entrainingfluid, such as high velocity air, that breaks the tube intomicrofilaments of 1 to 30 microns before solidifying.

The term “split fibers (also known as island in sea fibers) isrecognized by those having ordinary skill in the art and is intended toinclude those fibers produced by the processes of U.S. Pat. No.5,783,503 to Gillespie et al; U.S. Pat. No. 5,935,883 to Pike; and U.S.Pat. No. 5,290,626 to Nishioi et al. These patents are directed to theproduction of two component macrofibers that are produced using aspunbond or melt blown process. The two components are configured in asegmented pie mode alternating the polymers which are subsequently splitby hydraulic forces or natural separation with cooling. The twocomponents can also be configured as “islands in the sea” where finefibrils of one polymer are formed within a matrix polymer. The matrixpolymer is dissolved in solvent such as water, forming microfiberssmaller than 1.5 micron.

The term “electrospun fibers” is recognized by those having ordinaryskill in the art and includes those fibers produced by the processes ofU.S. Pat. No. 3,994,258 to Simm and U.S. Pat. No. 4,230,650 to Guignard.The processes provide methods to produce fibers from either a moltenpolymer or a polymer in a solution that is drawn within an electrostaticfield obtaining fine fibers of 2 to 5 microns.

Suitable polymers useful as synthetic microfibers for nonwoven, e.g.,carded nonwoven, media of the present invention include polymersdescribed above as well as various polymer resins, including but notlimited to, polyolefins such as polyethylene, preferably, polypropylene,polyisobutylene, and ethylene-alpha-olefin copolymers; acrylic polymersand copolymers such as polyacrylate, polymethylmethacrylate,polyethylacrylate, and preferably, esters thereof; vinyl halide polymersand copolymers such as polyvinyl chloride; polyvinyl ethers such aspolyvinyl methyl ether; polyvinylidene halides, such as polyvinylidenefluoride and polyvinylidene chloride; polyacrylonitrile; polyvinylketones; polyvinyl amines; polyvinyl aromatics such as polystyrene;polyvinyl esters, such as polyvinyl acetate; copolymers of vinylmonomers with each other and olefins, such as ethylene-methylmethacrylate copolymers, acrylonitrile-styrene copolymers, ABS resins,and ethylene-vinyl acetate copolymers; natural and synthetic rubbers,including butadiene-styrene copolymers, polyisoprene, syntheticpolyisoprene, polybutadiene, butadiene-acrylonitrile copolymers,polychloroprene rubbers, polyisobutylene rubber, ethylene-propylenerubber, ethylene-propylene-diene rubbers, isobutylene-isoprenecopolymers, and polyurethane rubbers; polyesters, such as polyethyleneterephthalate; polycarbonates; and polyethers.

The term “substantially uncharged” is intended to mean that thesynthetic microfiber, e.g., melt blown, polymer web need not be impartedwith an electrostatic charge to any degree that is intended to bepresent during any significant period of filtration, and that therecited filter characteristics are obtained, even, for example, when thefilter has been subjected to a liquid discharging rinse to reduce anycharge to its lowest residual level. It is understood, however, thatprocessing or manufacturing of the synthetic microfiber polymer fiberweb and/or the support materials used in conjunction with the syntheticmicrofiber material can impart a charge which can, in that case,initially enhance performance, but upon use as a filter, can be expectedto drop substantially and is therefore not considered in the discussionof threshold filter characteristics below. The resulting syntheticmicrofiber polymer fiber web can be uncharged, that is, such that nomeasurable charge associated with the synthetic microfiber web orcomposites thereof. In certain applications, the processed syntheticmicrofiber polymer fiber web or composites thereof can be treated,before filtration, to remove any charge that results from themanufacturing process. One exemplary charge-reducing treatment involvessoaking the fiber web in an alcoholic solution, e.g., about 99%isopropyl alcohol and 1% dioctylphthalate (DOP), to remove any residualcharge from the fiber web.

The fact the filter media is “substantially uncharged” is advantageousbecause the filter media relies on mechanical filtration, notelectrostatic properties, to achieve its performance. As a result,filtration performance is substantially consistent, without anyreduction in efficiency as a result of electrostatic charge decay.Accordingly, the alpha value of the filter media remains stable orconstant at approximately 11, 12, 13 or 14 throughout filtration.

It is believed that the present filter media provides enhanced airfiltration properties over current filter media by control over thesynthetic microfiber, e.g., melt blown, polymer web fiber diameter. Someof the current ASHRAE filter media products do contain some type of afibrous layer(s). However, most of these fibrous layers have largerfiber diameters, e.g., 2 microns or greater, and often include bindersor other additives within the fibrous structure. Many conventionalASHRAE filter media are also charged, e.g., electrostatically or byformation of electrets. The present invention demonstrates that controlof the fiber diameter provides an advantage over currently availablematerials. In general the fiber diameter of the synthetic microfiber webis maintained below 1.5 microns and is generally in the range of betweenabout 0.8 to about 1.5 microns. In a preferred embodiment, the fiberdiameter is maintained such that the average fiber diameter is about 1.0microns. It is believed that the high surface area of the finelyenmeshed synthetic microfibers of the present invention provides anefficient means to remove air borne contaminants without the need forcharge additives or electrostatic charge within the filter media.

One way to control the efficiency of the synthetic microfiber web is tocontrol the web basis of the web. The diameter of the fibers of thesynthetic microfiber material is between about 0.8 to about 1.5 microns,preferably between about 0.9 and 1.5 microns with a most preferreddiameter of about one micron, as measured by scanning electronmicroscopy. Optical measurements can appear of somewhat largerdimension, but the fine fibers should be under several microns. In apreferred embodiment, the synthetic microfiber polymeric material ispolypropylene, although other materials, and even materials such aspolyethylene, polybutylene and/or any other polymers which do notinherently possess a charge, such a nylons, can be serviceable. Oneexample of a suitable polypropylene material is available from ExxonCorporation as Exxon PP3456G, a proprietary polypropylene resincomposition which contains approximately 0.06 to 0.12 percent of anantioxidant, about 475-690 ppm peroxide, 35-70 ppm of a neutralizer, andhas a melt flow of about 1200. The fine fiber web has a weight basis ofbetween about 6 g/m² and about 25 g/m², e.g., 8 g/m², 18 g/m², or 22g/m², and has an alpha value, as measured after elimination of anyresidual electrostatic charge, of at least about 11, i.e., 13 or 14. Ina particularly preferred embodiment, the polymer fiber web has athreshold alpha value which remains substantially constant over timeafter eliminating any residual electrostatic charge. The fine fiberfilter media of the present invention can be fabricated in a range,e.g., with particle penetrations of 60-65 percent ASHRAE, 80-85 percentASHRAE, or 90-95 percent ASHRAE, while still achieving the combinationof effective filtration for the level of pressure drop.

The web basis weight of the polymer fiber web will vary depending uponthe requirements of a given filtering application. In general, higherweb basis weights yield better filtration, but there exists a higherresistance, or pressure drop, across the filter barrier when the filtermedia has a higher basis weight. In general the pressure drop across thefilter media is typically in the range of approximately 4-5 mm H20 for ahigh efficiency 90-95% filter at 10.5 fpm airflow velocity, andtypically 3-4 mm, and 1-2 mm for filters having 80-85 and 60-65%efficiencies, respectively. These efficiencies, or particle penetrationrates are achieved in the present invention with a low pressure dropbacking or support, and the synthetic microfiber fine fiber layer asdescribed herein, where the basis weight of the fine fiber layer is theprimary variable for affecting efficiency while achieving a high baselevel of alpha. One of ordinary skill in the art can readily determinethe optimal web basis weight, considering such factors as the desiredfilter efficiency and permissible levels of resistance. Furthermore, thenumber of plies of the polymer fiber web used in any given filterapplication can also vary from approximately 1 to 10 plies. One ofordinary skill in the art can readily determine a number of plies to beused. In a typical application, the filter media web is formed into abag for insertion into the airflow duct, and several bags can be placedin series for some applications.

Filter performance is evaluated by different criteria. It is desirablethat filters, or filter media, be characterized by low penetrationacross the filter of the contaminants to be filtered. At the same time,however, there should exist a relatively low pressure drop, orresistance, across the filter. Penetration, often expressed as apercentage, is defined as follows:Pen=C/C ₀where C is the particle concentration after passage through the filterand C₀ is the particle concentration before passage through the filter.Filter efficiency is defined as100−% PenetrationBecause it is desirable for effective filters to maintain values as lowas possible for both penetration and pressure drop across the filter,filters are rated according to a value termed alpha (α), which is theslope of log penetration versus pressure drop across the filter. Steeperslopes, or higher alpha values, are indicative of better filterperformance. Alpha is expressed according to the following formulaα=−100 log (C/C ₀)/DP,where DP is the pressure drop across the filter. As noted above, this istypically a few mm of H₂O.

In many filtering situations it is important to have a high initialalpha value. However, it is equally, if not more important, to maintainacceptable alpha values well into the filtration process. Decaying alphavalue is, as noted above, a problem often encountered in certainfiltration procedures. In many instances it is thus important to achieveacceptable alpha values well into the filtering process. Some standardtests for evaluating filter performance focus on penetration andresistance (as related by alpha value) after 200 milligrams of loading.Alpha decay is generally not a problem in filtering gases that containonly solids. In fact, in such filtering applications the alpha valueoften increases over time. The phenomenon of alpha decay is more evidentwhile filtering gases that contain liquid droplets or a mixture ofliquid droplets and solid particles.

In another embodiment, the present invention pertains to filter mediawhich includes a substantially uncharged synthetic microfiber, e.g.,melt blown, web and a support spun bond fiber layer. The diameter of thesynthetic microfibers of the web is between about 0.8 to about 1.5microns, preferably about 1.0 microns, and the spun bond fiber layeracts as a support and has a basis weight of between about 5 g/m² and 10g/m², preferably, about 8.5 g/m² when used as a carrier/cover layer(Snow Filtration, Cincinnati, Ohio, distributor for BBA Nonwovens. The8.5 g/m² spunbond is purchased from the German facility of BBANonwovens. Other spun bonds of various grades can be obtained throughSnow Filtration at their sites at Washougal, Wash. or Simpsonville,S.C.). A second spun bond layer can also be provided, in which case itcan have a greater basis weight to increase its overall strength. Thesecond spun bond layer can have a basis weight between about 34 g/m² andabout 55 g/m², i.e., 40.8 g/m² and about 54.4 g/m²). Typically the spunbond material is selected from polyesters, polyethylene, polypropylene,or polyamide polymers, and is assembled with the fine fiber layer suchthat the filter media composite has an alpha value of about 11 or more,i.e., 13 or 14. In a preferred embodiment, the spun bond layer is madeof a polypropylene resin manufactured by Reemay. For example, apreferred polypropylene spun bond support With a basis of weight of 40.8g/m² is fabricated from TYPAR 3121N (fiber diameter of between about 5and about 20 microns) (Reemay, Old Hickory, Tenn.) and for apolypropylene spun bond support with a basis weight of about 54.4 g/m²is fabricated from TYPAR 3151C (fiber diameter of between about 5 andabout 20 microns)(Reemay, Old Hickory, Tenn.).

The second spun bond layer can itself carry another synthetic microfiberlayer, which is preferably a coarse fiber blow melt layer formed in amanner similar to that of the fine fiber layer, but with substantiallycoarser fibers to form a prefilter/support layer. When this constructionis used, the two spun bond webs can be laminated together, with the finesynthetic microfiber layer and the coarse synthetic microfiber layersfacing each other to form a single, multilayer web that is integrallyjoined in a single process line assembly operation to form the finishedfilter media. Typically the spun bond material selected from materialssuch as polyesters, polyethylene, polypropylene, or polyamide polymers,is calendared to provide a strong, thin continuous surface on which thesynthetic microfiberous filter material is carried. The syntheticmicrofiber fiber material is deposited onto the spun bond material.Preferably, the filter media composite has an alpha value of at leastabout 11, i.e., 13 or 14. The average fiber diameter of the spun bondfibers can be between about five microns and about twenty five microns,preferably between about 5 microns and about 20 microns, most preferablybetween about 5 microns and about 15 microns. In a preferred embodiment,the synthetic microfiber is a melt blown fiber.

In general, a useful basis weight for the spun bond support when used toreceive the melt-blown fine fiber filter layer is between about 5 g/m²and about 10 g/m², preferably about 8.5 g/m². However, the basis weightof the support layer can vary depending upon the strength requirementsof a given filtering application, and considerably heavier spun bondlayers can be used as described above. One of ordinary skill in the artcan readily determine the suitable basis weight, considering suchfactors as the desired level of strength during manufacture or use,intended filter efficiency and permissible levels of resistance orpressure drop. However, in general, the spun bond layer is a relativelythin layer of coarse fibers that primarily serves a structural function,and is to contribute little or nothing to either filtration or pressuredrop in the completed web. Spun bond materials are readily available andwidely recognized in the art, and this component requires no furtherdiscussion.

To prepare suitable filter media useful for ASHRAE applications, thespun bond support is contacted to the synthetic microfibers withpressure blown fibers to adhere to the support and the two materials tobecome enmeshed with each other. The bond between the two layers ismechanical and no bonding agents are required.

Filter fabrication and the range of variation within the constructionparameters for the filter media of the present invention will be betterunderstood following discussion of a representative method ofmanufacture. Skipping ahead briefly to FIG. 4, there is shown anexemplary method and system 100 for manufacture of filter media having afine fiber filter layer in accordance with the present invention. Asshown, a base resin 101 is mixed in a mixer 102 and is passed to asupply hopper from which an extruder screw feeds the base materialthrough appropriate screens to a melt pump 103 which injects it at highpressure into a die body to be extruded from a plurality of apertures inthe die. Additives can be added in the mixer, such as solids orconditioners of various sorts can be added in the mixer, althoughpreferably for forming the fine fiber as described for a basic aspect ofthe present invention, neither solids nor ACRAWAX are added.

In the exemplary embodiment, a die having 35 apertures per inch ofapproximately 12.5 mil diameter was used and the material isprogressively heated along its path to exit the apertures at elevatedtemperature into a fast air knife or stream of heated air. The flowingair stretches the fibers to a diameter under several microns, andpreferably in the range of 1.0 microns, and carries the hot thin fiberstream across a gap 109 to a collector assembly. The collector assemblyincludes a traveling collector belt 110 moving over a suction box 111 sothat the heated thinned fine fibrous material is forced down onto thebelt 110. As noted above, preferably the belt carries a spun bond layerso that the fine fibrous material lands on top of the spun bond layerand contacts it with sufficient pressure to become mechanically joinedtherewith. Thus, the basic process forms a two layer mat having a finefibrous synthetic microfiber filter layer over a spun bond supportlayer. The air carrier stream at the extrusion nozzle is preferablyheated to about 570 degrees Fahrenheit for the described polypropyleneresin, so the stretched thin fibers landing on the spun bond carrier aretacky and adhere well upon contact. As noted above, the spun bond layercan have a significantly greater fiber diameter and serves to form a webhaving sufficient continuity to build the fine filter bed, andsufficient mechanical strength for subsequent handling and use.

As further illustrated in FIG. 4, the web so made is separated from thetraveling conveyor belt 110 and can pass to further stations foradditional treatments known in the art. These additional treatments canincludes steps such as electrostatic treatment in a treatment stationsuch as a plasma chamber or corona gap 112. The web can then pass to awinder 113 for bulk rolling or to other assemblies of known type forcutting, processing or packaging into specific filter units.

Equipment similar to system 100 can be used to form a coarse fibersupport layer, by melt blowing a coarse fiber material onto a similarspun bond support web. In the embodiments discussed below, the coarsefiber prefilter or support layer can utilize an extrusion head andheated air knife or airstream directed across the nozzles to producefibers having a 12-15 micron diameter which can, for example bedeposited in a layer as a tangled depth filter layer 40-60 mils thick onthe spun bond support. The coarse web so formed can feed in parallel tothe web produced by the fine filter fabrication system 100, with the twosynthetic microfiber layers contacting each other to join in afour-layer web having the two spun bond layers facing outwardly, and thesynthetic microfiber filter layers sandwiched therebetween. These can bejoined by physical pressure, with or without application of moderate,non-destructive, heat.

The invention also contemplates that finished filter media webs ofvarious types can be assembled using the basic two layer constructionproduced by the assembly 100. In addition, filters of differentefficiency can be made using the fine fiber layer while still achievinga sustained level of alpha of at least about 11, i.e., 13 or 14, overextended use. The different constructions employ different layers in thebasic web, as well as different basis weights of the fiber layers.However, in general, by reducing the basis weight of the fine fiberlayer in a given construction, a filter web of lower efficiency isproduced while still maintaining a level of alpha of at least about 11,i.e., 13 or 14.

As shown in FIG. 1, filter media composite 10 includes a spun bond layer12 and a substantially uncharged melt blown polymer fiber web 14 whichis mechanically joined to the spun bond layer 12. The melt blown polymerfine fiber web 14 can be deposited with a basis weight of about 6 g/m²to about 25 g/m² (grams per square meter) on the support, with the basisweight varied to produce higher or lower efficiency filters. In general,this construction has been found to produce practical and improvedfilter media for the higher-efficiency applications, having filterefficiency above 60%. The thickness of the spun bond layer 12 isgenerally about four or five mils, being a thin calendered support oflittle filtration power. Typically the final thickness of the filtercomposite as described for the various Figures amounts to a fabric-likeweb of between about 0.025 and 0.125 inches.

The combination of the synthetic microfiber web with the spun bond fiberlayer is unique in that no bonding agents, e.g., adhesives, are requiredto adhere the two materials to each other. Typically, the two layers arepressed together by a calendering process which causes each layer tophysically adhere to the other layer. This provides the advantage that abonding agent is not incorporated into the composite and does not effectthe porosity of the composite filter media.

In still another embodiment, the present invention pertains to filtermedia which includes a substantially uncharged synthetic microfiber,e.g., melt blown, polymer fiber web, at least one spun bond layer, and acoarse support fiber layer as described in the discussion of FIG. 4above. In one such embodiment 10 a, as shown in FIG. 3, a first spunbond layer 12 a forms the upstream layer of the filter media. A coarsesupport fiber layer 16 is immediately adjacent and downstream of thefirst spun bond layer 12 a. Downstream and adjacent coarse support fiberlayer is the fine synthetic microfiber, e.g., melt blown, polymer layer14. Finally, a second spun bond layer 12 b provides a downstream backinglayer. The overall thickness of filter media 10 a is about 0.100 inch,but can be varied by applying more or less mass loading in layer 14 fordifferent filter efficiencies. The web basis weight of the first spunbond layer can be between about 34 g/m² and about 55 g/m², while for thesecond spun bond layer the web basis weight can be between about 5 g/m²and about 10 g/m², preferably about 8.5 g/m². As noted above, this spunbond layers can be made from a variety of materials, includingpolyesters, polyolefins, and polyamides.

The fine synthetic microfiber polymer layer is as described above. Thatis, this layer is comprised of substantially uncharged finepolypropylene fibers having a diameter in the range of about 0.8 to 1.5μm, as measured by SEM, with one embodiment having an average diameterof about 1.0 μm.

The coarse layer 16 can also be comprised of a polypropylene, with thefiber diameter in the range of about 5 to about 20 microns, e.g., 13-17μm, i.e. 13-15 μm. The base resin can include ACRAWAX and otheradditives. The web basis weight of the coarse polypropylene layer can beabout 20 g/m² to about 100 g/m², preferably about 80 g/m² to provideeffective body with some prefiltration and minimal pressure drop. Apolypropylene resin with a melt flow index of 400 is preferred, althoughthose resins with melt flow indexes up to and including 1200 can be usedto prepare the coarse polypropylene layer. For example, a suitablepolypropylene resin with a melt flow of 1200 is the polypropylene resinPP3546G, available from Exxon (Houston, Tex.). Preferably, apolypropylene resin having a melt flow of 400 is available from MontellPolymers (Wilmington, Del.), designated as HH441. The present inventionalso provides constructions with greater thicknesses of the coarsesynthetic microfiber filter layer. In each case, the use of a syntheticmicrofiber fine fiber layer to achieve a stable and high level of alphaby mechanical filtration is used to produce a filter of greater than 50%efficiency, and preferably the fine fiber layer is specificallycontrolled to result in a level such as 60-65%, 80-85% or 90-95% ASHRAEfiltration of the desired airflow, with an base alpha value of at leastabout 11, e.g., at least 13, preferably at least 14, over the usefullife of the filter.

It is understood that the basis weight of the various layers will varydepending upon the requirements of a given filtering application. One ofordinary skill in the art can readily determine the optimal basisweight, considering such factors as the desired filter efficiency andpermissible levels of resistance. Furthermore, the number of plies ofthe support used in any given filter application can also vary fromapproximately 1 to 10 plies. The two-layer web of FIG. 1 can be useddirectly in applications such as respirators and breathing masks havinga short lifetime and an extrinsic supporting structure such as a screen,while the four-layer construction of FIG. 3 is preferred for bag filtersof large airflows in a commercial or industrial setting. Multiple layersof the basic web are appropriate for some applications to optimizefiltration, lifetime, service intervals or other factors of thefiltration system. One of ordinary skill in the art can readilydetermine the optimal number of plies to be used.

The coarse fiber support can include various additives conventionallyused in such materials to impart special properties, facilitateextrusion or otherwise improve performance of the material. One suitableadditive is a charge stabilizing additive. Examples of chargestabilizing additives include fatty acid amides derived from fattyacids. The term “fatty acid” is recognized by those having ordinaryskill in the art and it is intended to include those saturated orunsaturated straight chain carboxylic acids obtained from the hydrolysisof fats. Examples of suitable fatty acids include lauric acid(dodecanoic acid), myristic acid (tetradecanoic acid), palmitic acid(hexadecanoic acid), stearic acid (octadecanoic acid), oleic acid((Z)-9-octadecenoic acid), linoleic acid ((Z,Z)-9,12-octadecadienoicacid), linolenic acid ((Z,Z,Z)-9,12,15-octadecatrienoic acid) andeleostearic acid (Z,E,E)-9,11,13-octadecatrienoic acid). Typically theamides formed from the above referenced acids are primary amides whichare prepared by methods well known in the art. Secondary and tertiaryfatty acid amides can also be suitable as charge stabilizing agentswherein the amide nitrogen is substituted with one or more alkyl groups.Secondary and tertiary fatty acid amides can also be prepared by methodswell known in the art, such as by esterification of a fatty acidfollowed by an amidation reaction with a suitable alkylamine. The alkylsubstituents on the amide nitrogen can be straight chain or branchedchain alkyl groups and can have between about two and twenty carbonatoms, inclusive, preferably between about two and 14 carbon atoms,inclusive, more preferably between about two and six carbon atoms,inclusive, most preferably about two carbon atoms. In a preferredembodiment, the fatty acid amide can be a “bis” amide wherein an alkylchain tethers two nitrogens of two independent amide molecules. Forexample, alkylene bis-fatty acid amides include alkylenebis-stearamides, alkylene bis-palmitamides, alkylene bis-myristamidesand alkylene bis-lauramides. Typically the alkyl chain tether includesbetween about 2 and 8 carbon atoms, inclusive, preferably 2 carbonatoms. The alkyl chain tether can be branched or unbranched. Preferredbis fatty acid amides include ethylene bis-stearamides and ethylenebis-palmitamides such as N,N′-ethylenebistearamide andN,N′-ethylenebispalmitamide.

In certain embodiments, the charge stabilizing additive, e.g., a fattyacid amide, can be present within the coarse fiber support at aconcentration in the range of about 1.0 to 20% by weight. A preferredconcentration for the fatty acid amide charge stabilizing additive ispreferably about 1.0%. The ranges of concentrations intermediate tothose listed are also intended to be part of this invention, e.g., about2.5% to about 17%, 4.0% to about 15%, and about 6.0% to about 12.0% byweight. For example, ranges of concentration using a combination of anyof the above values recited as upper and/or lower limits are intended tobe included, e.g., 1% to about 6%, 2.5 to about 12%, etc.

One type of useful charge stabilizing additive, as noted above, arefatty acid amides. Examples of preferred fatty acid amides includestearamide and ethylene bis-stearamide. An exemplary stearamide iscommercially available as UNIWAX 1750, available from UniChemaChemicals, Inc. of Chicago, Ill. ACRAWAX® C is an ethylenebis-stearamide which is commercially available from Lonza, Inc. of FairLawn, N.J. ACRAWAX® C contains N,N′-ethylenebissteramide (CAS No.110-30-5) and N,N′-ethylenebispalmitamide (CAS No. 5518-18-3) with amixture of C-14 to C-18 fatty acid derivatives (CAS No. 67701-02-4) withan approximate ratio of 65/35/2(N,N′-ethylenebissteramide/N,N′-ethylenebispalmitamide/mixture of C-14to C-18 fatty acid derivatives) by weight. For example, the commercialproduct includes N,N′-ethylenebisstearamide, N,N′-ethylenebispalmitamidewith C14-C18 fatty acids. In certain embodiments of the invention,either N,N′-ethylenebisstearamide or N,N′-ethylenebispalmitamide can bethe sole charge stabilizing additive. In another embodiment, the ratioof a C14-C18 fatty acid can be varied from between about 0 to 20% basedon the total amount of the bisamides. In still other embodiments,mixtures of N,N′-ethylenebisstearamide and N,N′-ethylenebispalmitamidewhich fall in the range between about 0 to 100% for each bisamide can beutilized as additive mixtures, e.g., 80/20, 70/30, 5/50, etc.

To prepare suitable filter media useful for ASHRAE applications, thecoarse fiber support is contacted to the substantially unchargedsynthetic microfiber web and pressure is applied to the two layers,thereby causing the fibers of the two materials to become enmeshed witheach other. The bond between the two layers is mechanical and no bondingagents are required.

As shown in FIG. 2, filter media composite 10 includes a coarse fiberlayer 16 and a melt blown polymer fine fiber web 14 which ismechanically entwined with coarse fiber layer 16. The thickness of thecoarse fiber layer 16 is generally between about twenty and about onehundred mils, preferably about eighty or ninety mils. Typically thefinal thickness of the filter composite 10 is between about 0.025 inchesand about 0.125 inches as depicted in FIG. 2, although the describedconstruction can also be implemented with thicker support/prefilterlayers or thinner total web thickness.

The combination of the synthetic microfiber, e.g., melt blown, web withthe coarse synthetic microfiber, e.g., melt blown, layer is unique inthat no bonding agents or adhesives, are required to adhere the twomaterials to each other. Similarly, the melt deposition of either of thesynthetic microfiber layers onto the spun bond carrier is a solvent-freeprocess. Typically, the two synthetic microfiber layers on theirsupports are pressed together between rollers which causes each layer tophysically adhere to the other layer. This provides the advantage that abonding agent is not incorporated into the composite and does not effectthe porosity of the composite filter media.

The present invention also pertains to filter media which include afirst coarse 16 support fiber layer, a substantially uncharged syntheticmicrofiber, e.g., melt blown, polymer fiber web 14, a coarse supportfiber layer 16 and a spun bond support 12 fiber layer as shown in FIG.3. It should be understood that additional layers of each material canbe included to form the final filter media composite. Selection of howmany layers of each layer can be determined by the requirements of theapplication and by the skilled artisan.

For example, melt blown fibers are collected on a support layer 16 toform the fibrous filtration layer 14 with the finer fibers of thefibrous filtration layer 14 lying predominately adjacent the backinglayer 16 and the coarser fibers of the fibrous filtration layer 16 lyingpredominately adjacent the upstream surface 12 of the fibrous filtrationlayer 12 thereby providing a fibrous filtration composite 10 whichranges from coarser fibers at the upstream surface 12 to finer fibers 14at the backing layer 16. An additional support layer 16 can be added tothe downstream surface of 14 to provide additional support, and thislayer is naturally present when manufactured as described above by blowdeposition on a carrier web such as the spun bond web of FIG. 4.

When the upper surface of the fibrous filtration layer 12 functions asthe upstream, intake or dirty side of the fibrous filtration layer 12 inthe composite filter media 10, the coarser fibers in this less denseportion of the fibrous filtration layer 12 at and adjacent the upstream,intake or dirty side of the filter media serve as a pre-filter, catchingand retaining the largest particles from the air, gas or other fluidstream being filtered and thereby preventing these particles fromclosing the smaller voids between the finer fibers in the more denseportion of the fibrous filtration layer 12 at and adjacent the backinglayer 16. Thus, the collection of the coarser fibers at and adjacent theupstream surface 14 of the fibrous filtration layer 14 increases thedirt-holding capacity of the fibrous filtration layer 14 and thecomposite filter media 10 and the collection of the finer melt blownfibers 14 at and adjacent to the backing layer 16, increases thefiltration efficiency of the melt blown filtration layer 14 and thecomposite filter media 10.

The filter media of the present invention, therefore, provideefficiencies of filtration for air borne contaminants of at least60-65%, more preferably 80-85% and most preferably between 90-95% withan alpha value of at least 11, i.e., at least 13, preferably 14, basedon the removal of total air borne particulates in the unfiltered air.This is a significant improvement over current products which havesimilar efficiencies but which have lower alpha values of between about7 and 8.

The substantially uncharged synthetic microfiber, e.g., melt blown,filter web can be prepared by equipment built by J&M Laboratories,Dawsonville, Ga., and the melt blown can be made of Exxon 3546Gpolypropylene resin. A melt blown fiber web can be made at a throughputof about 3 lb/hr/inch width, with an average fine fiber diameter beingabout 1 microns. A suitable machine forms 74 inch wide web, and can usea lightweight polypropylene spunbond support. Samples tested for dustremoval capacity showed a high alpha, with the finer fiber sizesoffering stable and excellent filtration characteristics free of extremealpha decays experienced with charged filter media.

The following examples serve to further describe the invention.

EXAMPLES

TABLE I Fine fiber designed to make ASHRAE filters with improvedfiltration performance after IPA/DOP soak. 80-85% 80-85% with with TYPARTYPAR EFFICIENCY LEVEL 90-95% 3121 N 3151C 60-65% Air Flow Resistance5.0 3.39 3.43 1.52 (mmH₂O @ 10.5 FPM) NaCl Penetration 25.34 33.38 30.3770.4 (% @ 10.5 FPM) AFTER IPA/DOP SOAK ALPHA AFTER IPA/DOP 11.92 14.115.1 10.0 SOAK

The 90-95% ASHRAE material was prepared with 34 g/m² polypropylene spunbond as a first supporting layer and a second spun bond polypropylenesupporting layer of 8.5 g/m². PP3546G (1200 MF resin) was used in acoarse layer at 100 g/m², with a fine fiber layer blown onto the coarselayer at 24 g/m². The average fiber diameter of the fine fibers wasabout 1 micron.

The 80-85% ASHRAE material was prepared with TYPAR 3121N (fiber diameterof 5-20 μm) and TYPAR 3151C (fiber diameter of 5-20 μm) as the backingmaterial. HH441 (400 MF resin) was used in a coarse layer at 80 g/m²,with a fine fiber layer blown onto the coarse layer at 22 g/m². Theaverage fiber diameter of the fine fibers was about 1 micron.

The 60-65% ASHRAE material was prepared with 34 g/m² polypropylene spunbond as a first supporting layer and a second spun bond polypropylenesupporting layer of 8.5 g/m². PP3546G (1200 MF resin) was used in acoarse layer at 100 g/m², with a fine fiber layer blown onto the coarselayer at 8 g/m².

Table 1 demonstrates that increased alphas are achieved by using a veryfine fiber melt blown (approximately 1 micron measured by SEM). It isnoted that the 60-65% ASHRAE material has an alpha value ofapproximately 10. This lower value is due to the minimal amount of finefiber used in the composite filter and can be increased with additionalfine fiber material.

TABLE II Scrim Type: 0.45 oz/sy white spunbond Base Resin: Exxon 100%,PP3546G (polypropylene) PHYSICAL PROPERTIES Avg Min Max Std Dev N Weightg/m² 14.6 19 1.52 8 CNR mils 128.88 128 133 1.83 8 Thickness Air cfm27.50 26.5 28.5 1.00 2 Porosity NaCl @ 32 5.29 4.51 6.14 0.64 8Resistance lpm NaCl % @ 32 17.69 13.4 20.6 2.20 8 Penetration lpmCALCULATIONS NaCl Alpha @ 32 lpm 14.2150883 Fiber Diameter 1.1 micronsFluidity  0.0207528 Uncomp. Thickness 43.8904683 “N” represents thenumber of tests performed.

The melt blown resin fine fiber (Exxon PP3546G, polypropylene) wasproduced by extruding the molten material maintained at about 570° F.through a die tip maintained at 575° F. onto Typar 3121 (40 g/m²). Theprocess air attenuating the fiber was also maintained at 575° F.Throughput was approximately 0.27 grams per hole per minute. The die isconfigured as a hollow 86 inch long triangular bar into which the moltenresin is fed. At the apex of the triangle, there are 0.0125 inch drilledholes (diameter) with 35 holes per inch of die face. This configurationresults in a throughput of approximately 107 lb/hr of molten resinthrough the die.

TABLE III Scrim Type: 0.45 oz/sy white spunbond Base Resin: Exxon 100%,PP3546G (polypropylene) PHYSICAL PROPERTIES Avg Min Max Std Dev N Weightg/m² 16.44 14.5 19 1.52 8 CNR mils 129.88 128 133 1.83 8 Thickness AirPorosity cfm 27.50 26.5 28.5 1.00 2 NaCl @ 32 5.29 4.51 6.14 0.64 8Resistance lpm NaCl % @ 17.69 13.4 20.6 2.20 8 Penetration 32 lpmCALCULATIONS NaCl Alpha @ 32 lpm 14.21508826 With Scrim Fiber Diameterμm 1.369367851 Solidity — 0.015381195 Fluidity — 0.019078658 Uncomp. mm46.74869126 Thickness Without Scrim Fiber Diameter μm 2.034507332Solidity — 0.037276356 Fluidity — 0.061005998 Uncomp. mm 32.27178716Thickness

The melt blown resin fine fiber (Exxon PP3546G, polypropylene) wasproduced by extruding the molten material maintained at about 570° F.through a die tip maintained at 575° F. onto Typar 3121 (40 g/²). Theprocess air attenuating the fiber was also maintained at 575° F.Throughput was approximately 0.27 grams per hole per minute. The die isconfigured as a hollow 86 inch long triangular bar into which the moltenresin is fed. At the apex of the triangle, there are 0.0125 inch drilledholes (diameter) with 35 holes per inch of die face. This configurationresults in a throughput of approximately 107 lb/hr of molten resinthrough the die.

TABLE IV Scrim: 0.45 oz/sy white spunbond Resin: Exxon 99%, PP3548GAdditive: Lonza 1%, Acrawax C PHYSICAL PROPERTIES Avg Min Max Std Dev NWeight g/m² 47.05 43.06 53.39 3.55 6 C&R mils 24.50 21 29 7.57 6Thickness NaCl @ 32 3.65 3.48 3.82 0.12 6 Resistance lpm NaCl % @ 33.0029.3 36.4 2.57 6 Penetration 32 lpm

The melt blown resin fine fiber (Exxon PP3546G, polypropylene) wasproduced by extruding the molten material maintained at about 570° F.through a die tip maintained at 575° F. onto Typar 3121 (40 g/m²). Inthis example, 1% (by weight) of Acrawax C was blended into the moltenpolypropylene. The process air attenuating the fiber was also maintainedat 575° F. Throughput was approximately 0.27 grams per hole per minute.The die is configured as a hollow 86 inch long triangular bar into whichthe molten resin is fed. At the apex of the triangle, there are 0.0125inch drilled holes (diameter) with 35 holes per inch of die face. Thisconfiguration results in a throughput of approximately 107 lb/hr ofmolten resin through the die.

TABLE V Scrim: 0.45 oz/sy white spunbond Resin: Exxon 99%, PP3546GAdditive: Lonza 1%, Acrawax C PHYSICAL PROPERTIES Avg Min Max Std Dev NWeight g/m² 47.08 43.06 53.39 3.55 6 CNR mils 24.5 21 29 2.57 6Thickness Air cfm 33.15 31.6 34.7 1.55 2 Porosity NaCl @ 32 3.65 3.483.82 0.12 6 Resistance lpm NaCl % @ 33 29.3 36.4 2.57 6 Penetration 32lpm CALCULATIONS NaCl Alpha @ 32 lpm 13.191399 With Scrim Fiber Diameterμm 3.1123454 Solidity — 0.0444516 Fluidity — 0.0825011 Uncomp. mm46.327828 Thickness Without Scrim Fiber Diameter μm 3.5229855 Solidity —0.0731174 Fluidity — 0.1738757 Uncomp. mm 28.16495 Thickness

The melt blown resin fine fiber (Exxon PP3546G, polypropylene) wasproduced by extruding the molten material maintained at about 570° F.through a die tip maintained at 575° F. onto Typar 3121 (40 g/m²). Inthis example, 1% (by weight) of Acrawax C was blended into the moltenpolypropylene. The process air attenuating the fiber was also maintainedat 575° F. Throughput was approximately 0.27 grams per hole per minute.The die is configured as a hollow 86 inch long triangular bar into whichthe molten resin is fed. At the apex of the triangle, there are 0.0125inch drilled holes (diameter) with 35 holes per inch of die face. Thisconfiguration results in a throughput of approximately 107 lb/hr ofmolten resin through the die.

TABLE VI PHYSICAL PROPERTIES Avg Min Max Std Dev N g/m² 147.06 133 163.68.21 8 Thickness mils 194.68 191 198 2.50 8 Porosity cfm 24.90 24.4 25.40.05 2 Resistance @ 32 5.29 4.81 5.83 0.40 8 lpm Penetration % @ 3215.50 12.7 18.6 1.81 8 lpm CALCULATIONS NaCl Alpha @ 32 lpm 14.7853766Fiber Diameter μm 4.67236435 Solidity — 4.67236435 Fluidity — 0.04655431Uncomp. Thickness μm 137.890359

A melt blown resin fine fiber (Exxon PP3546G, polypropylene) wasproduced by extruding the molten material maintained at about 570° F.through a die tip maintained at 575° F. onto Typar 3121 (40 μm²). Theprocess air attenuating the fiber was also maintained at 575° F.Throughput was approximately 0.27 grams per hole per minute. The die isconfigured as a hollow 86 inch long triangular bar into which the moltenresin is fed. At the apex of the triangle, there are 0.0125 inch drilledholes (diameter) with 35 holes per inch of die face. This configurationresults in a throughput of approximately 107 lb/hr of molten resinthrough the die. This fine fiber was extruded onto a coarse melt blownlayer described as follows.

The coarse melt blown resin fiber (Exxon PP3546G, polypropylene) wasproduced by extruding the molten material maintained at about 570° F.through a die tip maintained at 520° F. onto an polypropylene spunbond(8.5 g/m²). The process air attenuating the fiber was also maintained at520° F. Throughput was approximately 2.26 grams per hole per minute. Thedie is configured as a hollow 86 inch long triangular bar into which themolten resin is fed. At the apex of the triangle, there are 0.0125 inchdrilled holes (diameter) with 35 holes per inch of die face.

The two melt blown composites were then plied together. This isreferenced as sample TR2527A.

TABLE VII PHYSICAL PROPERTIES Avg Min Max Std Dev N Weight g/m² 155.75137.7 169.2 11.51 8 CNR mils 153.00 105 194 40.61 8 Thickness Air cfm26.45 24.4 28.5 2.05 2 Porosity NaCl @ 32 3.26 4.57 3.98 0.38 8Resistance lpm NaCl % @ 32 15.75 13.7 19.2 1.84 8 Penetration lpmCALCULATIONS NaCl Alpha @ 32 lpm 14.99009229 Fiber Diameter μm4.679593913 Solidity — 0.034251033 Fluidity — 0.054456238 Uncomp.Thickness mm 198.8879333

A melt blown resin fine fiber (Exxon PP3546G, polypropylene) wasproduced by extruding the molten material maintained at about 570° F.through a die tip maintained at 575° F. onto Typar 3121 (40 g/m²). Theprocess air attenuating the fiber was also maintained at 575° F.Throughput was approximately 0.27 grams per hole per minute. The die isconfigured as a hollow 86 inch long triangular bar into which the moltenresin is fed. At the apex of the triangle, there are 0.0125 inch drilledholes (diameter) with 35 holes per inch of die face. This configurationresults in a throughput of approximately 107 lb/hr of molten resinthrough the die. This fine fiber was extruded onto a coarse melt blownlayer described as follows.

The coarse melt blown resin fiber (Exxon PP3546G, polypropylene) wasproduced by extruding the molten material maintained at about 570° F.through a die tip maintained at 520° F. onto a polypropylene spunbond(8.5 g/m²). In this example, 1% (by weight) of Acrawax C was blendedinto the molten polypropylene. The process air attenuating the fiber wasalso maintained at 520° F. Throughput was approximately 2.26 grams perhole per minute. The die is configured as a hollow 86 inch longtriangular bar into which the molten resin is fed. At the apex of thetriangle, there are 0.0125 inch drilled holes (diameter) with 35 holesper inch of die face.

The two melt blown composites were then plied together. This isreferenced as sample TR2527B.

TABLE VIII PHYSICAL PROPERTIES Std Avg Min Max Dev N Weight g/m² 147.18123.6 172.8 15.84 8 CNR Thickness mils 84.50 72 100 10.27 8 Air Porositycfm 30.05 28.5 31.5 1.55 2 NaCl Resistance @ 32 lpm 4.90 3.89 5.44 0.468 NaCl Penetration % @ 32 lpm 24.66 21.5 20.0 3.03 8 CALCULATIONS NaClAlpha @ 32 lpm 13.2094058 Fiber Diameter μm 5.069208513 Solidity —0.04370031 Fluidity — 0.075082098

A melt blown resin fine fiber (Exxon PP3546G, polypropylene) wasproduced by extruding the molten material maintained at about 570° F.through a die tip maintained at 575° F. onto Typar 3121 (40 g/m²). Inthis example, 1% (by weight) of Acrawax C was blended into the moltenpolypropylene. The process air attenuating the fiber was also maintainedat 575° F. Throughput was approximately 0.27 grams per hole per minute.The die is configured as a hollow 86 inch long triangular bar into whichthe molten resin is fed. At the apex of the triangle, there are 0.0125inch drilled holes (diameter) with 35 holes per inch of die face. Thisconfiguration results in a throughput of approximately 107 lb/hr ofmolten resin through the die. This fine fiber was extruded onto a coarsemelt blown layer described as follows.

The coarse melt blown resin fiber (Exxon PP3546G, polypropylene) wasproduced by extruding the molten material maintained at about 570° F.through a die tip maintained at 520° F. onto a polypropylene spunbond(8.5 g/m²). The process air attenuating the fiber was also maintained at520° F. Throughput was approximately 2.26 grams per hole per minute. Thedie is configured as a hollow 86 inch long triangular bar into which themolten resin is fed. At the apex of the triangle, there are 0.0125 inchdrilled holes (diameter) with 35 holes per inch of die face.

The two melt blown composites were then plied together. This isreferenced as sample TR2527C.

TABLE IX PHYSICAL PROPERTIES Avg Min Max Std Dev N Weight g/m² 159.49136.5 172.7 12.95 8 CNR mils 150.25 108 198 35.15 8 Thickness Air cfm28.00 27.5 26.5 0.05 2 Porosity NaCl @ 32 4.90 4.12 5.75 0.50 8Resistance lpm NaCl % @ 32 24.55 19.1 28 3.14 8 Penetration lpmCALCULATIONS NaCl Alpha @ 32 lpm 12.4384095 Fiber Diameter μm Solidity —Fluidity —

A melt blown resin fine fiber (Exxon PP3546G, polypropylene) wasproduced by extruding the molten material maintained at about 570° F.through a die tip maintained at 575° F. onto Typar 3121 (40 g/m²). Inthis example, 1% (by weight) of Acrawax C was blended into the moltenpolypropylene. The process air attenuating the fiber was also maintainedat 575° F. Throughput was approximately 0.27 grams per hole per minute.The die is configured as a hollow 86 inch long triangular bar into whichthe molten resin is fed. At the apex of the triangle, there are 0.0125inch drilled holes (diameter) with 35 holes per inch of die face. Thisconfiguration results in a throughput of approximately 107 lb/hr ofmolten resin through the die. This fine fiber was extruded onto a coarsemelt blown layer described as follows.

The coarse melt blown resin fiber (Exxon PP3546G, polypropylene) wasproduced by extruding the molten material maintained at about 570° F.through a die tip maintained at 520° F. onto a polypropylene spunbond(8.5 g/m²). In this example, 1% (by weight) of Acrawax C was blendedinto the molten polypropylene. The process air attenuating the fiber wasalso maintained at 520° F. Throughput was approximately 2.26 grams perhole per minute. The die is configured as a hollow 86 inch longtriangular bar into which the molten resin is fed. At the apex of thetriangle, there are 0.0125 inch drilled holes (diameter) with 35 holesper inch of die face.

The two melt blown composites were then plied together. This isreferenced as sample TR2527D.

TABLE X PHYSICAL PROPERTIES Avg Min Max Std Dev N Weight g/m² 110.61102.9 124.4 6.66 9 CNR mils 88.33 75 100 7.21 9 Thickness Air cfm 59.8057.7 61.9 2.10 3 Porosity NaCl @ 32 0.71 0.58 0.89 0.10 9 Resistance lpmNaCl % @ 32 82.37 73 86.4 3.64 9 Penetration lpm CALCULATIONS NaCl Alpha@ 32 lpm 11.6659872 Fiber Diameter μm 5.92011845 Solidity — 0.03389048Fluidity — 0.05369381 Uncomp. Thickness mm 142.772678

In this example, only the coarse melt blown resin fiber (Exxon PP3546G,polypropylene) was produced by extruding the molten material maintainedat about 570° F. through a die tip maintained at 520° F. onto apolypropylene spunbond (8.5 g/²). The process air attenuating the fiberwas also maintained at 520° F. Throughput was approximately 2.26 gramsper hole per minute. The die is configured as a hollow 86 inch longtriangular bar into which the molten resin is fed. At the apex of thetriangle, there are 0.0125 inch drilled holes (diameter) with 35 holesper inch of die face.

TABLE XI PHYSICAL PROPERTIES Avg Min Max Std Dev N Weight g/m² 112.94 99136.5 9.33 16 CNR mils 121.00 89 156 19.43 16 Thickness Air Porosity cfm273.20 269.8 276.6 3.40 2 NaCl @ 32 0.50 0.3 0.71 0.11 16 Resistance lpmNaCl % @ 32 34.86 78.1 89 3.28 16 Penetration lpm CALCULATIONS NaClAlpha @ 32 lpm 14.3529388 Fiber Diameter μm 12.9848733 Solidity —0.03710027 Fluidity — 0.06051716 Uncomp. Thickness mm 133.170755

In this example, only the coarse melt blown resin fiber (Exxon PP3546G,polypropylene) was produced by extruding the molten material maintainedat about 570° F. through a die tip maintained at 520° F. onto apolypropylene spunbond (8.5 g/m²). In this example, 1% (by weight) ofAcrawax C was blended into the molten polypropylene. The process airattenuating the fiber was also maintained at 520° F. Throughput wasapproximately 2.26 grams per hole per minute. The die is configured as ahollow 86 inch long triangular bar into which the molten resin is fed.At the apex of the triangle, there are 0.0125 inch drilled holes(diameter) with 35 holes per inch of die face.

TABLE XII Isopropyl Alcohol/IPA electrostatic discharge testing GradeTR2527A TR2527B TR2527C TR2527D Roll # 0101 0102 0101 0102 0101 01020101 0102 NaCl 5.98 5.61 5.41 5.96 4.55 4.52 4.49 4.73 Resistance (mmH20@ 32 LPM) Before IPA NaCl 14.7 16.9 13.6 14 26 20.7 29.3 23.5Penetration (% @ 32 LPM) Before IPA NaCl 20.7 23.1 22.4 20.2 38 39.338.9 32.6 Penetration (% @ 32 LPM) After IPA DOP 48.2 49.3 49.4 46.865.8 59.7 63.6 63.6 Penetration (% @ 64 LPM) After IPA Alpha 11.5 11.312.6 14.7 9.0 9.0 9.1 10.3

TABLE XIII Scrim Type: 0.45 oz/sy white spunbond Base Resin: ExxonPP3546G, 100% (polypropylene) PHYSICAL PROPERTIES Avg Min Max Std Dev NWeight g/m² 37.20 34.9 38.3 1.97 8 CNR mils 25.50 23 29 2.15 8 ThicknessAir cfm 36.05 32.6 39.5 3.45 2 Porosity NaCl @ 32 4.42 3.77 5.13 0.48 8Resistance lpm NaCl % @ 32 23.26 19.3 26.7 2.69 8 Penetration lpmCALCULATIONS NaCl Alpha @ 32 lpm 14.33309451 Fiber Diameter μm2.723976872 Solidity — 0.038422218 Fluidity — 0.063539903 Uncomp.Thickness mm 42.35728004

The melt blown resin fine fiber (Exxon PP3546G, polypropylene) wasproduced by extruding the molten material maintained at about 570° F.through a die tip maintained at 575° F. onto Typar 3121 (40 g/m²). Theprocess air attenuating the fiber was also maintained at 575° F.Throughput was approximately 0.27 grams per hole per minute. The die isconfigured as a hollow 86 inch long triangular bar into which the moltenresin is fed. At the apex of the triangle, there are 0.0125 inch drilledholes (diameter) with 35 holes per inch of die face. This configurationresults in a throughput of approximately 107 lb/hr of molten resinthrough the die.

TABLE XIV Scrim Type: 0.25 oz/sy pp Amoco spunbond Base Resin: Exxon99%, PP3548G and Lonza Acrawax C, 1% PHYSICAL PROPERTIES Avg Min Max StdDev N Weight g/m² 121.93 105.5 142.9 9.42 20 CNR mils 92.66 75 109 9.7220 Thickness Air Porosity cfm 300.20 243.4 357 56.80 2 NaCl @ 32 0.470.36 0.57 0.05 20 Resistance lpm NaCl % @ 32 54.24 50.2 62.2 2.70 20Penetration lpm CALCULATIONS NaCl Alpha @ 32 lpm 56.548255541 FiberDiameter μm 14.26002388 Solidity — 0.038873143 Fluidity — 0.06457523Uncomp. Thickness mm 132.2040265

In this example, only the coarse melt blown resin fiber (Exxon PP3546G,polypropylene) was produced by extruding the molten material maintainedat about 570° F. through a die tip maintained at 520° F. onto apolypropylene spunbond (8.5 g/m²). In this example, 1% (by weight) ofAcrawax C was blended into the molten polypropylene. The process airattenuating the fiber was also maintained at 520° F. Throughput wasapproximately 2.26 grams per hole per minute. The die is configured as ahollow 86 inch long triangular bar into which the molten resin is fed.At the apex of the triangle, there are 0.0125 inch drilled holes(diameter) with 35 holes per inch of die face.

TABLE XV Scrim Type: 0.45 oz/sy white spunbond (15.3 g/m² scrim;meltblown weight approx. 18.5 g/m²⁾ Base Resin: Exxon 100%, PP3548GPHYSICAL PROPERTIES Avg Min Max Std Dev N Weight g/m² 33.8625 31.8 37.92.0432434 8 CNR mils 20.125 18 23 1.615356 8 Thickness Air cfm 45.0544.7 45.4 0.35 2 Porosity NaCl @ 32 3.415 3.06 3.89 0.2477902 8Resistance lpm NaCl % @ 32 10.30375 6.55 12.5 1.2377695 8 Penetrationlpm CALCULATIONS NaCl Alpha @ 32 lpm 28.002041 Fiber Diameter μm3.1700555 Solidity — 0.0511643 Fluidity — 0.1007797 Uncomp. Thickness mm28.951806

The melt blown resin fine fiber (Exxon PP3546G, polypropylene) wasproduced by extruding the molten material maintained at about 570° F.through a die tip maintained at 575° F. onto Typar 3121 (40 g/m²). Theprocess air attenuating the fiber was also maintained at 575° F.Throughput was approximately 0.27 grams per hole per minute. The die isconfigured as a hollow 86 inch long triangular bar into which the moltenresin is fed. At the apex of the triangle, there are 0.0125 inch drilledholes (diameter) with 35 holes per inch of die face. This configurationresults in a throughput of approximately 107 lb/hr of molten resinthrough the die.

TABLE XVI Scrim Type: 0.25 oz/sy pp Amoco spunbond Base Resin: Exxon99%, PP3548G and Lonza AcrawaxC, 1% PHYSICAL PROPERTIES Avg Min Max StdDev N Weight g/m² 121.93 195.5 142.9 4.42 20 CNR mils 92.55 76 103 9.7220 Thickness Air Porosity cfm 300.20 242.4 3.57 54.40 3 NaCl @ 32 0.470.36 0.57 0.03 20 Resistance lpm NaCl % @ 32 54.24 50.2 63.3 3.70 20Penetration lpm CALCULATIONS NaCl Alpha @ 32 lpm 58.64625568 FiberDiameter μm 14.260023988 Solidity — 0.038873445 Fluidity — 0.04457427Uncomp. Thickness mm 137.2040365

In this example, only the coarse melt blown resin fiber (Exxon PP3546G,polypropylene) was produced by extruding the molten material maintainedat about 570° F. through a die tip maintained at 520° F. onto apolypropylene spunbond (8.5 g/m²). In this example, 1% (by weight) ofAcrawax C was blended into the molten polypropylene. The process airattenuating the fiber was also maintained at 520° F. Throughput wasapproximately 0.27 grams per hole per minute. The die is configured as ahollow 86 inch long triangular bar into which the molten resin is fed.At the apex of the triangle, there are 0.0125 inch drilled holes(diameter) with 35 holes per inch of die face.

TABLE XVII PHYSICAL PROPERTIES Avg Min Max Std Dev Weight g/m² 145.1125131.3 155.9 7.22 CNR Thickness mils 76.375 64 103 13.16 Air Porosity @65.5 lpm 3.01625 2.46 3.69 0.30 NaCl Resistance % @ 65.5 30.2375 24.134.3 3.28 lpm NaCl Penetration % @ 65.5 70.3875 62.9 77.8 5.62 lpmCALCULATIONS NaCl Alpha @ 65.5 lpm 17.2 NaCl Alpha after @ 65.5 lpm 4.65IPA/DOP Testing of TR2527 A material.

TABLE XVIII Scrim Type: 0.25 oz/sy pp Amoco spunbond Base Resin: Exxon99%, PP3546G; Lonza Acrawax C, 1% PHYSICAL PROPERTIES Avg Min Max StdDev N Weight g/m² 121.93 105.5 142.9 8.42 20 CNR mils 92.55 76 109 9.7220 Thickness Air cfm 300.20 243.4 357 58.80 2 Porosity NaCl @ 32 0.470.36 0.57 0.05 20 Resistance lpm NaCl % @ 32 54.24 50.2 62.2 2.79 20Penetration lpm CALCULATIONS NaCl Alpha @ 32 lpm 56.64825568 FiberDiameter μm 14.26002388 Solidity — 0.038873145 Fluidity — 0.05457623Uncomp. Thickness mm 137.2040265 Testing of TR2526B material.

TABLE XIX Scrim Type: 0.45 oz/sy white spunbond (scrim weight 15.3 g/m²;meltblown approximately 8.5 g/m²) (fine layer only of Table XVII) BaseResin: Exxon 100%, PP3546G PHYSICAL PROPERTIES Avg Min Max Std Dev NWeight g/m² 24.11375 23.3 25.41 0.06 8 CNR mils 13.5 11 15 1.41 8Thickness Air cfm 173.6 150.5 186.7 13.10 2 Porosity NaCl @ 32 1.001250.73 1.26 0.15 8 Resistance lpm NaCl % @ 32 38.4375 32.7 43.9 3.12 8Penetration lpm

TABLE XX (90-95% ASHRAE) RUN 1 Scrim Being blown Onto: Typar 3121 Layerbeing collated in: TR2786A (Coarse fibered meltblown Prefilter) ResinBeing Used: PP3546G (Exxon Resin) Additives Being used: NONE Trial Name:TR2841A LOT: 0510129 TEST UNITS Average Minimum Maximum St. Dev. N BasisWeight (entire product) (g/m²) 150.28 127.4 176.5 10.33 48 Basis Weight(fine fiber only) (g/m²) 23.2 23.2 23.2 0  1 NaCl Resistance (mmH₂O @ 32LPM) 4.9 4.32 5.57 0.34 48 NaCl Penetration (% @ 32 LPM) 24.45 20.6 29.32.59 12 (after IPA/DOP soak) NaCl Alpha after IPA/DOP soak (Unitless)12.484105 Fiber Diameter (fine fiber only) (Microns) 1.02

TABLE XXI RUN 2 Scrim Being blown Onto: Typar 3121 Layer being collatedin: TR2786A (Coarse fibered meltblown Prefilter) Resin Being Used:PP3546G (Exxon Resin) Additives Being used: NONE Trial Name: TR2841ALOT: 0510295 TEST UNITS Average Minimum Maximum St. Dev N Basis Weight(entire product) (g/m²) 160.7 145.5 186.4 8.76 30 Basis Weight (finefiber only) (g/m²) 25.84 24.54 26.7 0.81  4 NaCl Resistance (mmH₂O @ 32LPM) 4.87 3.93 6 0.44 30 NaCl Penetration (% @ 32 LPM) 28.85 27.3 30.41.55  2 (after IPA/DOP soak) NaCl Alpha after IPA/DOP soak (Unitless)11.085301 Fiber Diameter (fine fiber only) (Microns) 1.14

TABLE XXII 80-85% ASHRAE RUN 1 Scrim Being blown Onto: Typar 3121 Layerbeing collated in: TR2786A (Coarse fibered meltblown Prefilter) ResinBeing Used: PP3546G (Exxon Resin) Additives Being used: NONE Trial Name:TR2785B LOT: 0510134 TEST Average Minimum Maximum St. Dev. N BasisWeight (entire product) (g/m²) 146.34 120.1 173.1 12.1 48 Basis Weight(fine fiber only) (g/m²) 19.3 19.3 19.3 0  1 NaCl Resistance (mmH₂O @ 32LPM) 3.4 2.5 4.28 0.43 48 NaCl Penetration (% @ 32 LPM) 40.5 38.2 483.23 12 (after IPA/DOP soak) NaCl Alpha after IPA/DOP soak (Unitless)11.54544 Fiber Diameter (fine fiber only) (Microns) 1.16

TABLE XXIII RUN 2 Scrim Being blown Onto: Typar 3121 Layer beingcollated in: TR2786A (Coarse fibered meltblown Prefilter) Resin BeingUsed: PP3546G (Exxon Resin) Additives Being used: NONE Trial Name:TR2785A LOT: 0510296 TEST Average Minimum Maximum St. Dev. N BasisWeight (entire product) (g/m²) 149.21 130.5 165.8 7.78 100 Basis Weight(fine fiber only) (g/m²) 19.78 17.2 22.8 1.62  11 NaCl Resistance (mmH₂O@ 32 LPM) 3.43 2.7 4.26 0.32 100 NaCl Penetration (% @ 32 LPM) 38 36.239.8 1.8  2 (after IPA/DOP soak) NaCl Alpha after IPA/DOP soak(Unitless) 12.251207 Fiber Diameter (fine fiber only) (Microns) 1.23

TABLE XXIV Coarse Fiber Meltblown Layer Used with Both 80-85% and 90-95%ASHRAE Products Scrim Being blown Onto: 0.25 oz/sy PolypropyleneSpunbond Layer being collated in: N/A Resin Being Used: PP3546G (ExxonResin) 98% of total meltblown Additives Being used: Lonza Acrawax C  2%of total meltblown Trial Name: TR2786A LOT: 0510285 TEST Average MinimumMaximum St. Dev. N Basis Weight (entire product) (g/m²) 88.84 74.5 109.87.55 150 Basis Weight (fine fiber only) (g/m²) N/A N/A N/A N/A N/A NaClResistance (mmH₂O @ 32 LPM) 0.33 0.14 0.53 0.07 150 NaCl Penetration (%@ 32 LPM) 53.31 44.5 66.5 4.07 150 (before IPA/DOP soak) NaCl Alphaafter IPA/DOP soak (Unitless) N/A Fiber Diameter (fine fiber only)(Microns) N/A

One skilled in the art will appreciate further features and advantagesof the invention based on the above-described embodiments. Accordingly,the invention is not to be limited by what has been particularly shownand described, except as indicated by the appended claims. Allpublications and references cited herein are expressly incorporatedherein by reference in their entirety.

1. A method of forming filter media, such method comprising the stepsof: extruding and melt blowing at least one fine fiber filter layer ontoa support layer, wherein the at least one fine fiber filter layer hasfibers with a diameter of less than about 1.5 microns and is depositedwith a basis weight effective to achieve filtration above 50% and analpha, as measured in a discharged condition, of at least about eleven.2. The method of claim 1, wherein the support layer is a spun bondsupport.
 3. The method of claim 1, wherein the at least one melt blownfine fiber layer is deposited on the spun bond support and adheredthereto in a heated state.
 4. The method of claim 1, wherein the supportlayer includes a coarse fiber prefilter.
 5. The method of claim 1,wherein the coarse fiber prefilter is mechanically adhered to the atleast one fine fiber filter layer.
 6. The method of claim 1, wherein thesupport layer is formed from fibers having a diameter in the range ofabout 5 microns to 15 microns.
 7. The method of claim 1, wherein the atleast one fine fiber filter layer has a web basis weight in the range ofabout 6 g/m² to 25 g/m².
 8. The method of claim 1, wherein the supportlayer has a web basis weight in the range of about 34 g/m² to 55 g/m².9. The method of claim 1, further comprising a pre-filter layer mated tothe support layer.
 10. The method of claim 1, further comprising thestep of charging the filter media to form an electret.
 11. A method offorming a filter media for use in heating, refrigeration, ventilation,and exhaust duct filtering applications, the method comprising the stepsof: extruding and melt blowing at least one microfiber polymer web ontoa support layer to form a mechanically bonded web, the microfiberpolymer web being formed of fine fibers having a diameter of less thanabout 1.5 microns; wherein the filter media has a base alpha value of atleast about 11 throughout the useful life of the filter media, evenafter decay of any charge that may be present.
 12. The method of claim11, wherein the support layer is a spun bond support.
 13. The method ofclaim 11, wherein the support layer includes a coarse fiber prefilter.14. The method of claim 11, wherein the support layer is formed fromfibers having a diameter in the range of about 5 microns to 15 microns.15. The method of claim 11, wherein the at least one microfiber polymerweb has a web basis weight in the range of about 6 g/m² to 25 g/m². 16.The method of claim 11, wherein the support layer has a web basis weightin the range of about 34 g/m² to 55 g/m².
 17. The method of claim 11,further comprising a pre-filter layer mated to the support layer. 18.The method of claim 11, further comprising the step of charging thefilter media to form an electret.